The objective of this proposal is to examine early and specific biochemical events in tumor promotion. First we shall develop an in vitro assay system to measure ribonucleic acid synthesis in nuclei isolated from mouse epidermis and cultured 3T3 fibroblasts. Using this biological assay to monitor the effects of phorbol myristate acetate (PMA), we will investigate the contributions of cellular components such as membrane and cytoplasmic fractions to the action of PMA. We will determine if cytoplasm from PMA treated tissue cells can stimulate RNA synthesis in isolated nuclei, and we will identify receptors or other cellular factors necessary for PMA activity. We will compare results obtained for PMA with those using other promoting agents, non-promoting analogues and promotion inhibitors, in order to clarify the specificity of the observed mechanisms to tumor promotion. The results obtained should increase knowledge of mechanisms of carcinogenesis, particularly with respect to the primary cellular site of action of tumor promoters. These results may be applicable to therapeutic strategies, and the identification of environmental carcinogens.